1. Field of the Invention
The present invention relates to a die for use in a plastic granulating apparatus of a so-called underwater cutting type for consecutively cutting strands extruded by the die into pellets by a rotating blade in a cutter box into which cooling water is circulatingly supplied.
2. Description of the Related Art
A description will be given of a conventional example of a die for use in a plastic granulating apparatus of the underwater cutting type. As shown in FIG. 6, a die 101 has a plurality of orifices 102 provided at intervals in an annular zone in which extruded strands can be cut by a rotating blade. Each orifice 102 has a large-diameter introducing hole 102a formed on an introducing surface 101a side of the die 101 and a small-diameter discharging hole 102b formed on a discharge surface 101b side thereof, thereby making it possible to extrude a strand of a predetermined outside diameter (pellet outside diameter).
With the above-described conventional technique, since the orifices are each formed by the large-diameter introducing hole and the small-diameter discharging hole, and are open in an annular zone of the die having a limited area, there is a limit to the number of orifices which can be provided at this annular zone having the limited area, and it is impossible to cope with the need for an increased capacity.
In addition, in the plastic granulating apparatus of the underwater cutting type, since cooling water is circulatingly supplied to a cutter box, the discharging surface of the die is exposed to cooling water. Hence, there is a possibility that clogging can occur due to the cooling and solidification of the molten plastic within the orifice. In a case where jackets for temperature regulation are disposed on the die to prevent the clogging, an interval between the orifices on both sides of each jacket must be made large, so that the so-called dead space occurs. As a result, there has been a problem in that the number of orifices which can be provided decreases.
The invention has been devised in view of the problem of the above-described conventional technique, and its object is to provide a die for use in a plastic granulating apparatus of the underwater cutting type which makes it possible to cope with the need for an increased capacity by providing numerous orifices by reducing the dead space occurring in areas where the jackets for temperature regulation are disposed.
To attain the above object, a plastic granulating apparatus of an underwater cutting type in accordance with the invention has a die for use in a plastic granulating apparatus of an underwater cutting type in which a predetermined area is provided in an annular shape on a discharging side surface of a die base material, and a plurality of nozzles whose open ends are formed as a multiplicity of orifices distributed over a substantially entire area of the predetermined area are respectively made to communicate with introducing slots in an introducing side surface of the die base material, characterized in that each of the nozzles has a small-diameter portion having a diameter smaller than an opening diameter of the orifice, and a jacket for temperature regulation is disposed at a depthwise position where the small-diameter portion is disposed.
In addition, a die for use in a plastic granulating apparatus of an underwater cutting type in which a predetermined area is provided in an annular shape on a discharging side surface of a die base material, and a plurality of nozzles whose open ends are formed as a multiplicity of orifices distributed over a substantially entire area of the predetermined area are respectively made to communicate with introducing slots in an introducing side surface of the die base material may be characterized in that each of the nozzles has an eccentric portion disposed eccentrically with respect to the orifice, and a jacket for temperature regulation is disposed at a depthwise position where the eccentric portion is disposed.
A space for a jacket for temperature regulation is secured as a small-diameter portion having a diameter smaller than the opening diameter of the orifice is provided at a predetermined depthwise position in the nozzle whose open end is formed as each orifice.
In addition, the space for a jacket for temperature regulation may be secured as an eccentric portion disposed eccentrically with respect to the orifice is provided at a predetermined depthwise position in the nozzle whose open end is formed as each orifice.
Since dead space occurring due to the provision of the jackets is reduced to increase the number of orifices in the discharging side surface of the die, and the discharging side surface having a limited area is thereby effectively utilized, it is possible to cope with the need for an increased capacity.
If the small-diameter portion of the nozzle is disposed eccentrically with respect to the orifice, the aforementioned dead space can be further reduced, and it is possible to make optimum use of the discharging side surface of the die.